Glyphosate (N-phosphonomethyl glycine) is well known as a highly effective and commercially important herbicide useful for combating the presence of a wide variety of unwanted vegetation, including agricultural weeds. Glyphosate is conventionally applied as a formulated product dissolved in water to the foliage of annual and perennial grasses and broadleaf plants and the like, is taken up over a period of time into the leaves, and thereafter translocates throughout the plant.
Usually, glyphosate is formulated in commercial compositions in the form of a water-soluble salt. Various salts of glyphosate, methods for preparing salts of glyphosate, formulations of glyphosate or its salts and methods of use of glyphosate or its salts for killing and controlling weeds and other plants are disclosed in U.S. Pat. No. 4,507,250 to Bakel, U.S. Pat. No. 4,481,026 to Prisbylla, U.S. Pat. No. 4,405,531 to Franz, U.S. Pat. No. 4,315,765 to Large, U.S. Pat. No. 4,140,513 to Prill, U.S. Pat. No. 3,977,860 to Franz, U.S. Pat. No. 3,853,530 to Franz, and U.S. Pat. No. 3,799,758 to Franz. The aforementioned patents are incorporated herein in their entirety by reference. Salts in commercial use include the ammonium salt, alkylamine salts, such as the isopropylamine salt, alkali metal salts, such as the sodium salt, and the trimethylsulfonium salt. However, formulations of glyphosate in its acid form are also used. The IPA salt is widely used in commercial glyphosate formulations. Typical glyphosate salt formulations include aqueous concentrates, requiring simple dilution and distribution in water for application by the end-user, and water-soluble or water-dispersible dry formulations, especially granules, requiring dissolution or dispersion in water prior to application.
A major advantage of the IPA salt over many other salts of glyphosate, such as the potassium salt, has been the good compatibility in aqueous solution concentrate formulations of that salt with a wide range of surfactants. As used herein, the term “surfactant” is intended to include a wide range of adjuvants that can be added to herbicidal glyphosate compositions to enhance the herbicidal efficacy thereof, as compared to the activity of the glyphosate salt in the absence of such adjuvant, irrespective of whether such adjuvant meets a more traditional definition of “surfactant.”
Potassium glyphosate concentrate compositions exhibit high specific gravity as compared to solutions of other glyphosate salts thereby allowing high unit per volume loading. For example, one liter of a 30% a.e. by weight glyphosate potassium salt solution at 20° C. contains approximately 376 g glyphosate a.e. per liter, whereas one liter of a 30% a.e. by weight glyphosate IPA salt solution at 20° C. contains approximately 347 g glyphosate a.e. per liter. In other words, at equal a.e. weight concentration, the potassium salt solution delivers about 8% more glyphosate a.e. per liter. It is likely however that serious consideration of glyphosate potassium salt as a herbicidal active ingredient has been inhibited by the relative difficulty in formulating this salt as aqueous solution concentrate (“SL”) formulations together with preferred surfactant types. For example, a widely used surfactant in glyphosate IPA salt compositions, namely polyoxyethylene (15) tallowamine of formula (3) above, is highly incompatible in aqueous solution with glyphosate potassium salt. PCT Publication No. WO 00/15037 notes the low compatibility of alkoxylated alkylamine surfactants in general with high-strength glyphosate concentrates.
Under most application conditions, the herbicidal efficacy of glyphosate can be significantly enhanced by including one or more surfactants in the composition to be applied. It is believed that such surfactants act partly by facilitating the penetration of glyphosate, a relatively hydrophilic compound, through the rather hydrophobic cuticle which normally covers the external above-ground surfaces of higher plants. The surfactant can be provided in the concentrate formulation, or it can be added by the end user to the diluted spray composition.
Surfactants tending to give the most useful enhancement of glyphosate herbicidal effectiveness are generally but not exclusively cationic surfactants, including surfactants which form cations in aqueous solution or dispersion at pH levels of around 4-5 characteristic of SL formulations of monobasic salts of glyphosate. Examples are long-chain (typically C12 to C18) ethoxylated tertiary alkylamine surfactants and quaternary alkylammonium surfactants. An especially common tertiary alkylamine surfactant used in aqueous solution concentrate formulations of glyphosate IPA salt is the very hydrophilic surfactant polyoxyethylene (15) tallowamine, i.e., tallowamine having in total about 15 moles of ethylene oxide in two polymerized ethylene oxide chains attached to the amine group.
A drawback of ethoxylated tertiary alkylamine surfactants known in the art is that when included in concentrate formulations at levels consistent with good herbicidal performance, they tend to be categorized as eye and skin irritants, have elevated oral and aquatic toxicity as compared to some other surfactants known in the art, and typically do not have a ready biodegradable classification. In some jurisdictions, aquatic toxicity or other environmental regulatory issues such as caution or warning labeling may dictate how much, if any, surfactant is incorporated in the compositions of the invention. In contrast, glyphosate has been found to have low animal toxicity because the enzyme system on which it acts is specific to plants. In the case of commercial glyphosate formulations, the ethoxylated tertiary alkylamine surfactants used as bioefficacy enhancers are typically more toxic than glyphosate.
A further drawback of ethoxylated tertiary alkylamine surfactants is they tend to form a stiff gel when combined with water which adds to the complexity and expense of manufacturing formulations containing such surfactants, by making it difficult to clean vessels and process piping. In practice, this problem is ameliorated by adding an anti-gelling agent, such as polyethylene glycol, to the surfactant.
A class of alkyletheramine, alkyletherammonium salt and alkyletheramine oxide surfactants has been disclosed in U.S. Pat. No. 5,750,468 to be suitable for preparation of aqueous solution concentrate formulations of various glyphosate salts, including potassium salt. It is disclosed therein that an advantage of the subject surfactants when used in an aqueous composition with glyphosate salts is that these surfactants permit the glyphosate concentration of the composition to be increased to very high levels. The oxide surfactants are also reported to have reduced eye irritancy.
Nonionic surfactants, such as for example alkylpolyglucosides (“APG”), are generally reported to be less effective in enhancing herbicidal activity than cationic or amphoteric surfactants when used as the sole surfactant component of SL formulations of glyphosate salt. Advantageously however, as compared to ethoxylated tertiary alkylamine surfactants, alkylpolyglucoside surfactants are generally classified as non-toxic and ready biodegradable. In particular, those surfactants are typically classified as having low oral toxicity, as being biodegradable with no potential for bioaccumulation, and as having no ecotoxicity. Those features are especially desirable because it minimizes exposure risks to the user and minimizes environmental impact.
The use of alkyl polyglucoside surfactants in glyphosate formulations creates other problems.
For example, the addition of such alkyl polyglucosides generally results in higher viscosity formulations (as compared to formulations without alkyl polyglucosides). Such an increase in the viscosity of these high-strength formulations is undesirable for various reasons. In addition to being more difficult to conveniently pour from the container or to wash residues therefrom, the deleterious effects resulting from higher viscosity formulations is more dramatically observed with respect to pumping requirements. Increasing volumes of liquid aqueous glyphosate products are being purchased by end-users in large refillable containers sometimes known as shuttles, which typically have an integral pump or connector for an external pump to permit transfer of liquid. Liquid aqueous glyphosate concentrates are also shipped in bulk, and in large tanks having a capacity of up to about 100,000 liters. The liquid is commonly transferred by pumping to a storage tank at a facility operated by a wholesaler, retailer or cooperative, from which it can be further transferred to shuttles or smaller containers for onward distribution. Because large quantities of glyphosate formulations are purchased and transported in early spring, the low temperature pumping characteristics of such formulations are extremely important.
In some commercial applications it is desirable to dye glyphosate formulations blue or green in order to distinguish the glyphosate product from other herbicidal products. However, glyphosate concentrate formulations comprising an alkylpolyglucoside (e.g., Agrimul™ APG-2067 and 2-ethyl-hexyl glucoside) surfactant, such as described in WO 00/15037, are generally dark brown in color having a color value of 14 to 18 as measured by a Gardner colorimeter. When dye is added to a formulated glyphosate product having a Gardner color greater than about 10, the concentrate remains dark brown in color.
Still further, alkylpolyglucoside surfactants are subject to foaming, especially during dilution, mixing and spraying of the formulation by the user. In many cases the foam is slow to dissipate.
There exists a need for a surfactant system for use as a pesticidal bioefficacy enhancer that is relatively non-toxic, non-irritating and ready biodegradable. Moreover, the surfactant system must be capable of being combined with a pesticide to form a stable pesticidal concentrate having pesticidal efficacy comparable to pesticidal compositions known except containing toxic and/or low biodegradable surfactant systems.